Recycling ammonium hydroxide-treated water in the production of polyacrylonitrile fibers



United States Patent C) RECYCLING AMMONIUM HYDROXIDE-TREATED WATER 1NTHE PRODUCTION OF POLYACRY- LONKTRILE FIBERS Louis S. Hovis, Cary, N.C.,Charles H. Apperson, Decatur, Ala, and William A. Blackburn, ChapelHilL, N.C., assignors to Monsanto Company, St. Louis, M0., a corporationof Delaware 7 No Drawing. Filed Aug. 27, 1963, Ser. No. 304,949 8Claims. (Cl. 264*38) This invention relates to the preparation ofacrylonitrile filaments and fibers. More particularly, this inventionrelates toa convenient and economical method of washing acrylonitrilefibers and filaments.

It is frequently a practice in the synthetic fiber industry to recoverthe process water used in spinning fibers and filaments. This processwater normally contains concentrations of acidic compounds which wouldbe detrimental to the fiber properties. It is well known that the effectof acids on synthetic fibers will lower the heat stability of the fiberand the fiber will undergo undesirable color changes when heated.

If the recovered process water used in spinning the fibers could berecycled and used again in the fiber producing process it would be veryadvantageous from an economic standpoint. Therefore, a neutralizingagent that could be added to the acid containing process water toneutralize the acids present and thus enable the reuse of the processwater would be desirable. In order for such a neutralizing agent to beeffective, the salts formed between the neutralizing agent and the acidspresent would have to be either washed out of the fiber by an additionalstep or else would have to be neutral salts.

It is an object of the invention to provide an improved economicalmethod for the production of acrylontrile fibers.

It is a further object of this invention to produce an acrylonitrilefiber of improved properties by the use of a neutralizing agent in thewash water which will reduce the detrimental influence of acids on thefiber properties.

Other objects and advantages of the present invention will becomeapparent from the following detailed description thereof and theappended claims.

Generally, the objects of this invention are accomplished by spinning anacrylonitrile fiber or filament and thereafter washing the thus producedfiber or filament with an acid contaminated wash water that has beentreated with ammonium hydroxide. This enables the process water used inthe production of the fibers to be recycled and used again aftertreatment with ammonium hydroxide.

The invention is applicable not only to polyacrylonitrile, but also tocopolymers, interpolymers, and blends thereof, particularly thosecontaining at least 80 percent by weight of polymerized or copolymerizedacrylonitrile. For example, the polymer may be a copolymer of from 80 to98 percent of acrylonitrile and from 2 to 20 percent of anothercopolymerizable mono-olefinic monomer.- Suitable copolymerizablemono-olefinic monomers include arcylic, alpha-chloroacrylic andmethacrylic acids, the acrylates, such as methyl methacrylate, ethylmethacrylate, butyl methacrylate, methoxymethyl methacrylate,beta-chloroe'thyl methacrylate, and the correspond- 3,318,983 PatentedMay 9, 1967 ing esters of acrylic and alpha-chloroacrylic acids; vinylchloride, vinyl fluoride, vinyl bromine, vinylidene chloride,l-chloro-l-bromoethylene; methacrylonitrile; acrylamide andmethacrylamide; alpha-chloroacrylamide, or monoalkyl substitutionproducts thereof; methyl vinyl ketone; vinyl carboxylate's, such asvinyl acetate, vinyl chloroacetate, vinyl propionate, and vinylstearate; N- vinylimides, such as N-vinylphthalimide andN-vinylsuccinimide; methylene malonic esters; itaconic acid and itaconicester; N-vinyl carbazole; vinyl furan; alkyl vinyl esters; vinylsulfonic acid; ethylene alpha, beta-dicarboxylic acids or theiranhydrides' or derivatives, such as diethylcitraconate,diethylmesaconate; styrene; vinyl naphthalene; vinyl substitutedtertiary heterocyclic amines such as the vinylpyridines andalkyl-substituted vinylpyridines for example, 2-vinylpyridine,4-vinylpyr'idine, Z-methyl-S-vinylpyridine, and the like;l-vinylim'idazole and alkyl-substituted l-vinylimidazoles, such as 2-,4-, or S-methyl-l-vinylimidazole, vinyl pyrro'lidone, vinylpiperidone,and other inono-olefinic copolymerizable monomeric materials.

The polymer can be a ternary interpolyrner, for example, productsobtained by the interpolymerization of acrylonitrile and two or more ofany of the monomers, other than acrylonitrile, enumerated above. Morespecifically, and preferably, the ,ternary polymers contain from 80 to98 percent of acrylonitrile, from 1 to 10 percent of a vinylpyridine ora l-vinylimidazole, and from 1 to 18 percent of another copolymerizablemono-olefinic' substance, such as methacrylonitrile, vinyl acetate,methyl methacrylate, vinyl chloride, vinylidene chloride, and the like.

The polymer can also be a blend of polyacrylonitrile or a copolymer offrom 80 to 99 percent acrylontrile and from 1 to 20 percent of at leastone other mono-olefinic copolymerizable monomeric substance with from 2to 50 percent of the weight of the blend of a copolymer of from 30 to 90percent of a vinyl substituted tertiary heterocyclic amine and from 10to percent of at least one other mono-olefinic copolymerizable monomer.Preferably, when the polymeric material comprises a blend, it will be ablend of from to 99 percent of a copolymer of 80 to 98 percentacrylonitrile and from 2 to 20 percent of another mono-olefinic monomer,such as vinyl acetate,

with from 1 to 20 percent of a copolymer of from 30 to percent of avinyl-substituted tertiary heterocyclic amine, such as vinylpyridine, al-vinylimidazole or a vinyl lactam, and from 10 to 70 percent ofacrylonitrile to give a blend having an overall vinyl-substitutedtertiary heterocyclic amine content of from 2 to 10 percent, based onthe weight of the blend.

While the preferred polymers employed in the instant invention are thosecontaining at least 80 percent acrylonitrile, generally recognized asthe fiber-forming acrylonitrile polymers, it will be understood that theinvention is likewise applicable to polymers, copolymers, interpolymersand blends containing less than 80 percent of acrylonitrile and as lowas 35 percent acrylonitrile. Polymers containing from about 35 to 80percent acrylonitrile may be copolymerized, interpolyinerized andblended with any of the mono-olefinic monomers enumerated herein. Forexample, the process is applicable to fibers acrylonitrile and 60percent vinyl chloride and to a tert. polymer of approximately 67percent acrylonitrile, 21 percent vinyl chloride and 12 percentvinylidene chloride.

The invention is further applicable to other vinyl polymers containing amajority of vinyl chloride, vinylidene chloride, styrene and other wellknown vinyl polymers and to copolymers, interpolymers and blends thereofwith the mono-olefinic monomers enumerated herein. For example, fi berswhich are formed from copolymers of vinyl chloride and vinylidenechloride, copolymers of vinyl chloride and vinyl acetate and copolymersof vinyl chloride and vinyl formate may be treated according to theprocedure of this invention.

In the preparation of acrylonitrile fibers and filaments, it is anecessary step after spinning the fiber, to wash the fiber in order toremove any residual polymer and solvent from the fiber. It would beadvantageous and economical to use the process water which was used inspinning the fibers in order to wash the prepared fiber. However, theprocess water frequently accumulates acidic compounds which have adetrimental effect on the fiber properties, such as lowering the heatstability of the fiber.

In addition, if residual acid in the fiber is high, it will also causecorrosion of textile processing equipment such as carding and knittingmachines. High residual acid in a fiber will cause the card teeth tocorrode to such a degree during processing that much of the fiber mustbe discarded and the equipment must be shut down and the rust must beremoved from the card teeth.

It has been found that the addition of ammonium hydroxide to the washwater is an effective way .to accomplish the neutralization of the acidsin the wash water and in addition does not require an additional washingstep to remove the salts that are formed. If a strong base is added to.the wash water to neutralize the acids present, then the fibers Washedwith the treated wash water have to undergo an additional wash step toremove the basic salts which will greatly effect the heat sensitivity ofthe fiber if allowed to remain on the fiber.

A further advantage to the use of ammonium hydroxide wash water isthatexcessive amounts of ammonium hydroxide, in addition to that amountrequired to neutralize the acids present, are surprisingly not harmful.It is believed that the excess of ammonium hydroxide is volatilized inthe form of ammonia and water upon drying the fiber.

In addition, the basic dye acceptance of fibers can be increased bywashing them with wash water neutralized with ammonium hydroxide ratherthan with city water. Calcium and magnesium ions contained in most citywaters block dye sites and thereby reduce the basic dye acceptance. Ithas been found that fiber washed with process water treated withammonium hydroxide resulted in gains up to 40 percent higher basic dyeacceptance as compared with fiber washed with water containing calciumand magnesium ions.

The ammonia may be added to the wash Water containing the acidicmaterials at any time prior to the Washing of the fiber. The ammonia maybe added as ammonia gas, liquid ammonia or any form of ammonia that willresult in the formation of ammonium hydroxide. The concentration ofammonium hydroxide in the wash water may be varied to give a treatedWater having a pH from about 7.0 to a pH of about 10.0. Where thetreated water is recycled and used to wash fiber several times, the pHof the water must be readjusted after each use. Excessive amounts of theammonium hydroxide are not harmful and additional washing steps toremove the salts formed are not required.

The neutralizing agent in the form of ammonium hydroxide, ammonia gas,and the like, is added to the wash water at room temperature andthoroughly mixed with the wash water. The wash water may then be used towash the prepared fiber.

The invention will be more fully described with reference to thefollowing examples demonstrating the prep- EXAMPLE 1 Two thousand eighthundred and fifty grams of dimethylacetamide containing 2 percent byweight of acetic acid was chilled to -5 C. To this chilled composition,950 grams of an acrylonitrile copolymer comprising 93 percent ofacrylonitrile and 7 percent vinylacetate and having a specific viscosityof 0.151 was added. The materials were slurried for minutes at 350 rpm.The slurry was then transfer-red to a spinning machine and spun into aspin bath comprising 55 percent of dimethylacetamide containing 2percent acetic acid and 45 percent water to produce fiber. The fiber wasthen washed with wash water recovered from the preparation of similarfiber. The wash water contained about 0.07 percent by weight of aceticacid and had a pH of 3.6. The col-or, heat stability and basic dyeacceptance of the fiber Washed as described above is shown in the tablebelow. It was found that fiber washed as described above causedundesirable corrosion on the card used in the normal processing offibers. The test for card corrosion was conducted by running a sampleinto the carding machine, shutting the machine down and allowing it tostand overnight. Since the fiber contained acetic acid, the machinewould not start up again the next morning.

EXAMPLE 2 a This water was analyzed and found to contain 20 ppm.

of calcium, 2 p.p.m. of magnesium, 6 ppm. of sodium and potassium, and1.5 p.p.m. of heavy oxides. The color, heat stability and basic dyeacceptance of the fiber washed as described above is shown in the tablebelow.

EXAMPLE 3 Wash water was prepared by adding grams of glacial acetic acidto approximately 50 gallons of deionized water in a stainless steeldrum. The acetic acid and the water were mixed by recirculating themixture for approximately 5 minutes. The wash water had an acetic acidcontent of about 0.07 percent by weight. Ammonium hydroxide was added tothe wash water in an amount sufficient to give the wash water a pH of9.25. This wash water was used to wash fiber prepared according to theprocedure of Example 1. The color and heat stability of the fiber washedas described above is shown in the table below.

EXAMPLE 4 Wash water was prepared by adding 140 grams of glacial aceticacid to approximately 50 gallons of deionized water in a stainless steeldrum. The acetic acid and the water were mixed by recirculating themixture for approximately 5 minutes. The wash water had an acetic acidcontent of about 0.07 percent by weight. Ammonium hydroxide was added tothe Wash Water in an amount sufiicient to give the wash water a pH of8.0. This wash water was used to wash fiber prepared according toprocedure of Example 1. The color, heat stability and basic dyeacceptance of the fiber washed as described above is shown in the tablebelow.

The color results indicative of heat stability used throughout theexamples consist of measurement of purity and brightness as calculatedfrom the tristimulus values determined on a General Electricspectrophotometer by the methods recommended by the Standard O-bserverand Coordinate System of the International Commision of Illumination, asfully set forth in the Handbook of Colorimetry, published by theTechnology Press, Massachusetts Institute of Technology, in 1936. All ofthe measurements given were made on crimped, annealed, and carded staplesamples made from skeins of 200 wraps of 3.0 denier per filament fiber.

The basic dye acceptance (BDA) values given in the table below wereobtained by mixing 25 ml. of a bufiercd (pH=5.2) solution of Sevron Blue2G dye with 0.6 grams of fiber in a sealed tube at 100 C. for 2 hours.The exhausted dyebath was then analyzed spectrophotometrieally todetermine the amount of dye remaining and the percentage of dye uptakeon the fiber.

The following table shows a comparison of the color and heat stabilityof the fiber washed in the various examples set forth above.

COLOR, HEAT STABILITY AND BASIC DYE ACCEPT- ANCE TABLE.

Initial Color Heated Color (145 C. for

25 min.)

P BR

Percent;

Example 1. 0 Example 2. Example 3. 2

Example 4 BR represents brightness and P represents purity above.

As many variations of this invention may be made without departing fromthe spirit and scope thereof, it is intended that the invention belimited solely by the scope of the appended claims.

We claim:

1. In a process for the preparation of fibers from vinyl polymerswherein a vinyl polymer is dissolved in a solvent therefor which maycontain an acid contaminant, the resulting homogeneous solution isextruded into a coagulating medium which may contain an acid contaminantto produce fibers, and said fibers are subsequently Washed with anaqueous solution, the improvement which comprises treating said aqueoussolution used in the preparation of said fibers with ammonium hydroxidewhen said aqueous solution is contaminated with acid and then using thethus treated aqueous solution in washing additional fibers.

2. In a process for the preparation of fibers from vinyl polymerswherein a vinyl polymer is dissolved in a solvent therefor which maycontain an acid contaminant, the resulting homogeneous solution isextruded into a coagulating medium which may contain an acid contaminantto produce fibers, and said fibers are subsequently washed with anaqueous solution, the improvement which comprises treating said aqueoussolution used in the prepara tion of said fibers with ammonium hydroxidewhen sait aqueous solution is contaminated with acid to give 2 solutionhaving a pH of from about 7.0 to about 10.0 anc then using the thustreated aqueous solution in washing additional fibers.

3. The process as defined in claim 2 wherein the viny polymer is anacrylonitrile polymer.

4. The process as defined in claim 3 wherein the acrylonitrile polymeris a copolymer of at least percen acrylonitrile and up to 20 percent ofvinyl acetate.

5. In a process for the preparation of fibers from vinyi polymerswherein said polymer is dissolved in a solvent therefor which maycontain acetic acid, the resulting homogeneous solution is extruded intoa coagulating medium which may contain acetic acid to produce fibers,and said fibers are subsequently washed With an aqueous solution, theimprovement which comprises treating said aqueous solution used in thepreparation of said fibers with ammonium hydroxide when said aqueoussolution contains acetic acid and then recycling the thus treatedaqueous solution for use in washing additional fibers.

6. In a process for the preparation of fibers from vinyl polymerswherein said polymer is dissolved in a solvent therefor which maycontain acetic acid, the resulting homogeneous solution is extruded intoa coagulating medium to produce fibers, and said fibers are subsequentlywashed with an aqueous solution, the improvement which comprisestreating said aqueous solution used in the preparation of said fiberswith ammonium hydroxide when said aqueous solution contains from about0.01 to about 0.10 percent by Weight of acid to provide a solutionhaving a pH of about 7.0 to about 10.0 and then recycling the thustreated aqueous solution for use in washing additional fibers.

7. The process as defined in claim 6 wherein the vinyl polymer is anacrylonitrile polymer.

8. The process as defined in claim 7 wherein the acrylonitrile polymeris a copolymer of at least 80 percent acrylonitrile and up to 20 percentof vinyl acetate.

References Cited by the Examiner UNITED STATES PATENTS 2,553,483 5/1951Sowter 264-38 2,723,900 11/1955 Hooper 264182 2,916,348 12/ 1959Cresswell 2641 82 ALEXANDER H. BRODMEARKEL, Primary Examiner.

F. S. WHISENHUNT, D. J. ARNOLD,

Assistant Examiners.

1. IN A PROCESS FOR THE PREPARATION OF FIBERS FROM VINYL POLYMERSWHEREIN A VINYL POLYMER IS DISSOLVED IN A SOLVENT THEREFOR WHICH MAYCONTAIN AN ACID CONTAMINANT, THE RESULTING HOMOGENEOUS SOLUTION ISEXTRUDED INTO A COAGULATING MEDIUM WHICH MAY CONTAIN AN ACID CONTAMINATTO PRODUCE FIBERS, AND SAID FIBERS ARE SUBSEQUENTLY WASHED WITH ANAQUEOUS SOLUTION, THE IMPROVEMENT WHICH COMPRISES TREATING SAID AQUEOUSSOLUTION USED IN THE PREPARATION OF SAID FIBERS WITH AMMONIUM HYDROXIDEWHEN SAID AQUEOUS SOLUTION IS CONTAMINATED WITH ACID AND THEN USING THETHUS TREATED AQUEOUS SOLUTION IN WASHING ADDITIONAL FIBERS.